When the Lancastrians lost, he took the necessary oaths to the likes of Richard III but his reputed promise to defend Wales for his king with such ferocity that an invader must needs “make his entrance and irruption over my belly” was discharged in a ceremony equally literary and lawyerly — when he stood under a bridge while his invading ally, the Welsh-descended Henry Tudor, marched over it.

There’s always a loophole when one fails to insist on direct language.

Together the two would win the crown for Henry — and in a sense very much win it for Wales — at Bosworth Field, where Gruffydd is sometimes credited personally with the blow that felled King Richard.

He lived on to 1525, a loyal supporter of Henry VII and his son Henry VIII. But the reciprocal gratitude of the kings did not outlive Gruffydd’s passing, for the Welsh offices that he designed to pass to his grandson Rhys ap Gruffydd were instead foisted on Water Devereux, Baron Ferrers.*

The consequent hostility would set Rhys on his way to the block. In 1529, our man drew a blade on Devereux, and their respective bands of retainers skirmished violently with each other over succeeding months.

Attempting to elevate his frustrated political claim by assuming the name “Fitz Urien” — in reference to a half-legendary ancient Welsh king — finally got him clapped in the Tower. His subsequent trial on a fanciful charge of conspiring with Scotland to form a Celtic league against the English asserted the central royal authority against a noble loose cannon who also happened to be part of the Catholic, anti-Anne Boleyn faction; at a stretch it could arguably** be read to make him one of the earliest victims of the still-nascent English Reformation. Be that as it may, his countrymen did not much mourn the fall of a vaunting and greedy line, however spurious the grounds.

And indeed many men regarded his [Rhys’s] death as Divine retribution for the falsehoods of his ancestors, his grandfather, and great-grandfather, and for their oppressions and wrongs. They had many a deep curse from the poor people who were their neighbours, for depriving them of their homes, lands and riches. For I heard the conversations of folk from that part of the country that no common people owned land within twenty miles from the dwelling of Sir Rhys ap Thomas, that if he desired such lands, he would appropriate them without payment or thanks, and the disinherited doubtless cursed him, his children and his grandchildren, which curses in the opinion of many men fell on the family, according to the old proverb which says — the children of Lies are uprooted, and after oppression comes a long death to the oppressors. (Source)